1. Field of the Invention
The present invention relates to a power unit mount assembly.
2. Description of the Related Art
One power unit mount device equipped with a dynamic damper is disclosed in Japanese Utility Model Publication of Unexamined Application No. 58-44222. This mount device comprises annular external and internal cylindrical bodies with a resilient material such as rubber inserted between these two bodies. The external cylindrical body is mounted on the power unit through a bracket. The internal cylindrical body is mounted on the vehicle body. A projection is provided on the external circumferential surface of the external cylindrical body, at a location opposite the bracket. In this projection, a mass member is installed so that an elastic member is positioned between the projection and the mass member. That is, the mass member is resiliently supported by the external cylindrical body at a portion remote from the bracket, and functions as dynamic damper.
In this type of fabrication, the power unit is resiliently supported on the vehicle body while at the same time receiving the action of the mass member as a dynamic damper. As a result, it is possible to shift from the resonant frequency of the mount device of 200 to 400 Hz to a frequency band where the problem of the vibrational sound entering the vehicle body does not occur.
In this type of conventional mount device, because the mass member is resiliently supported on the external cylindrical body to avoid resonance at a specific frequency, the resonant frequency, fo, obtained by the formula ##EQU1## is reduced to the low frequency side through the reduction of the k value or the increase of the m value, so that there is a restraint on the set degrees of freedom of the resonant frequency, fo. For example, it is essentially impossible to set a resonance point in the low frequency range of 6 to 50 Hz, and the problem exists that this type of conventional mounting device cannot be applied to the vibration damping of engine shake, etc.